This invention relates to a sheet feeder particularly useful in feeding batches of sheets and to a method of verifying batches of sheets.
In known batch sheet feeders, sheets may be fed singly from a stack through parallel belts and counted while they are transported through the parallel belts. The sheets are then either fed individually to a target (e.g., a box between flights of a downstream conveyor) so as to be stacked in batches directly on the target, or fed and stacked onto some sort of drop table (e.g., a reciprocating table) to be dropped vertically onto or into their target as a batch.
One drawback with singly feeding sheets to the target is that the target area must not move or be obstructed during the entire time that a given batch is being fed. By stacking the batch on a drop table, this problem is avoided in that the entire batch is dropped to the target together as one group. However, the speed at which the batch drops is fixed (by gravity) and the feeding of sheets to the table must halt for the time it takes the drop table to open, the product to drop and the table to return to its ready position. Another drawback is that the target must be able to accept the product from the top. With both approaches, a further difficulty in stacking the sheets is in controlling the trailing edge of a sheet so that the next sheet does not crash into it. This difficulty increases with the speed of feeding.
While known batch sheet feeders count sheets to ensure there is a proper number of sheets in each batch, in many applications the sheets of a batch are printed differently. Thus, each sheet of a batch may be unique in the batch. In such applications, another problem is ensuring that each batch has a proper set of sheets. Another drawback with the noted types of batch sheet feeder is that they have no mechanism to address this problem.
This invention seeks to provide a batch sheet feeder that avoids at least one of these drawbacks.
According to the present invention, there is provided a batch sheet feeder comprising: an upstream first conveyor section arranged to convey sheets singly in a downstream direction to a downstream second conveyor section; said second conveyor section comprised of an upper second conveying section and a lower second conveying section forming a gap therebetween, said gap being largest at an upstream end of said second conveyor section and diminishing in size toward a downstream end of said second conveyor section; and a gate positioned proximate said downstream end of said second conveyor section for selectively blocking sheets from exiting said second conveyor section.
According to another aspect of the invention, there is provided a batch sheet feeder, comprising: a lower endless conveyor; an upper endless conveyor arranged with respect to said lower conveyor so as to form a sheet feed path between said lower conveyor and said upper conveyor for feeding sheets in a downstream direction; said lower conveyor substantially paralleling said upper conveyor along an upstream first section, said lower conveyor jogging away from said upper conveyor at an upstream end of a downstream second section so as to form a gap between said lower conveyor and said upper conveyor at said second section that is larger than any gap between said lower conveyor and said upper conveyor at said first section.
According to a further aspect of the invention, there is provided a sheet feeder, comprising: a sheet conveyor; a sheet sensor; a visual attribute sensor having a field of view covering an area of said conveyor at a certain downstream location so as to sense an area of any sheet on said conveyor at said downstream location, said visual attribute sensor for comparing a sensed area of a sheet at said downstream location with a stored visual attribute.
According to another aspect of the present invention, there is provided a method of verifying batches of sheets, comprising: for each sheet at a given sheet position in each batch of sheets: obtaining a visual attribute for at least an area of said each sheet; comparing said visual attribute with a stored visual attribute; and selectively verifying said each batch based on said comparing.
According to a further aspect of the invention, there is provided a method of verifying batches of sheets, comprising: conveying sheets in a sheet conveyor; sensing sheets with a sheet sensor; sensing a visual attribute with a visual attribute sensor having a field of view covering an area of said conveyor at a certain downstream location so as to sense an area of any sheet on said conveyor at said downstream location; verifying batches of sheets at a processor receiving an output from said visual attribute sensor and said sheet sensor.
Other features and advantages of the invention will be apparent after reviewing the description in conjunction with the accompanying drawings.